The present invention relates to an apparatus for and a method of delivering a measured dose of medicament, typically a liquid or a powder in fluidised form, to a patient.
Nebulizers and inhalers have been developed for the delivery of medicament in a gas to a patient.
Inhalers broadly fall into two categories, these being pressurized metered dose inhalers (pMDI's) and dry powder inhalers (DPI's), which both have a mouthpiece through which a patient inhales. The effective use of inhalers can, however, prove difficult to a number of patients, notably paediatric patients.
With the traditional, or non breath-actuated, pressurized metered dose inhalers, this difficulty arises because effective operation of the inhaler requires a patient to actuate the inhaler at the onset of inhalation in order to draw the medicament deep into the lungs. Achieving this co-ordination is what is particularly difficult for paediatric patients. Typically, if the pressurized metered dose inhaler is actuated before the onset of inhalation most of the medicament will hit the back of the throat and if the pressurized metered dose inhaler is actuated after the onset of inhalation most of the medicament will remain in the throat or bronchial tracts where it will have no effect.
Breath-actuated pressurized metered dose inhalers and dry powder inhalers, whilst not requiring such co-ordination of actuation and inhalation, also prove difficult to use to paediatric patients because those inhalers require a patient to inhale with sufficient strength to achieve a particular flow rate, notably 30 l/min for dry powder inhalers, which in breath-actuated pressurized metered dose inhalers triggers the aerosol canister and in dry powder inhalers draws air through the inhaler. Paediatric patients in particular are not able to develop the necessary tidal volumes to achieve such flow rates. For paediatric patients, tidal volumes are typically in the range of from 10 to 150 ml giving rise to flow rates in the range of only from about 3 to about 15 l/min.
WO-A-96/01663 (in the name of Aradigm Corporation) and WO-A-97/07896 (in the name of Fluid Propulsion Technologies, Inc.) disclose examples of devices which have been developed to co-ordinate aerosol delivery with inhalation by a patient. Specifically, these devices are arranged to deliver an aerosol on sensing an inspiration flow rate above a specific minimum value.
To date, aerosols have been delivered to paediatric patients using a nebulizer or an inhaler in combination with a spacer. Whilst both of these systems provide a low velocity aerosol cloud which can be inhaled by a paediatric patient, usually over several breaths, the dose obtained by the patient can vary considerably and the patient has no indication as to the exact dose delivered.
This variability in dose stems essentially from the requirement for paediatric patients to use a face mask; paediatric patients being unable to grip a mouthpiece effectively. The use of a face mask, however, increases the dead space between the nebulizer or spacer and the patient. This is not usually a problem in adult patients as they generally have a tidal volume which far exceeds the dead space downstream of the nebulizer or spacer, and as such the dose received by the patient can be approximated with a fair degree of accuracy as the inhaled volume multiplied by the concentration of medicament in the gas.
WO-A-96/13294 (in the name of Medic-Aid et al) discloses an apparatus for and a method of delivering medicament to a patient for inhalation in which medicament is introduced into a chamber prior to inhalation and the total dose of medicament received by the patient is calculated based on the volume of the chamber, the amount of medicament introduced into the chamber, the time elapsed since the introduction of medicament into the chamber and the flow rate of gas drawn out of the chamber.
It is an aim of the present invention to provide an apparatus for and a method of delivering a measured dose of medicament more reliably and accurately to patients who develop only small tidal volumes and inhale only at low rates.